Warning: There were 2 warnings in `mutate()`.
The first warning was:
ℹ In argument: `graph_obj = map(...)`.
ℹ In group 1: `shrimp = "post-closure"`.
Caused by warning:
! `graph.adjacency()` was deprecated in igraph 2.0.0.
ℹ Please use `graph_from_adjacency_matrix()` instead.
ℹ Run `dplyr::last_dplyr_warnings()` to see the 1 remaining warning.Shrimp
Networks
All harvesters
- Pre-closure: 2009-2014
- Post-closure: 2016-2021
| Density | Modularity | |
|---|---|---|
| pre-closure | 0.4209184 | 0.1563785 |
| post-closure | 0.5348639 | 0.1793088 |
Shrimpers
| Density | Modularity | |
|---|---|---|
| pre-closure | 0.3129252 | 0.08896277 |
| post-closure | 0.3188776 | 0.09065861 |
Non-shrimpers
| Density | Modularity | |
|---|---|---|
| pre-closure | 0.337585 | 0.1553351 |
| post-closure | 0.5042517 | 0.1805972 |
Changes in portfolios of shrimp harvesters
Entry and exit
Post closure, shrimp (css, csc), lobster-apprentice under 18 (lau), and elver dip net fyke 1 (e6) are replaced by menhaden (menc, menr), spat, and aquaculture, all of which are new license categories and don’t necessarily represent a shift in fisheries.
The proportion of licenses held by shrimpers didn’t appear to change dramatically by those who chose to continue in fisheries. Lobster was still the dominant target species by these harvesters.
Difference in difference estimator
Did the closure of the shrimp fishery impact the number of licenses held by harvesters?
# A tibble: 4 × 5
term estimate std.error statistic p.value
<chr> <dbl> <dbl> <dbl> <dbl>
1 (Intercept) 1.30 0.0520 25.0 1.06e-18
2 shrimp_harvester 1.47 0.0736 20.0 1.75e-16
3 closure 0.0972 0.0688 1.41 1.71e- 1
4 did -0.499 0.0973 -5.13 3.02e- 5
According to the DiD estimator, the closure did negatively impact those shrimpers in a statistically significant way. It may be worth noting that a significant number of harvester left fisheries entirely after the moratorium and we may need to figure out a way to incorporate exit and entry in the difference-in-difference estimation.